An arterial blood gas syringe is used in obtaining an arterial blood sample from a patient. The arterial blood sample is then inputted or transferred to a blood gas analyzer to analyze the gas components of the blood sample. The concentration of known gas components in the blood sample is useful in diagnosing the condition of the patient.
A number of differently configured arterial blood gas samples have been advanced or devised for drawing the arterial blood sample from the patient. Current commercially available arterial blood gas syringes include elements commonly found in syringes, namely, a syringe barrel, a sealing plug and a plunger rod. The sealing plug is connected to the tip of the plunger rod and is used in defining a blood receiving space within the syringe barrel. Such syringes are also characterized by the use of filter media connected to the sealing plug or plunger rod. Generally, the filter acts to permit air to pass from the blood receiving space while preventing the flow of blood past the sealing plug. The differences among the various prior art syringes lie primarily in the design or construction of the sealing plug, although there are syringes that differ in plunger rod construction. In connection with devising an arterial blood gas syringe including a filter, it is desirable to achieve a relatively rapid fill time of the blood receiving space, while avoiding or minimizing the time associated with the unwanted diffusion of gas into the obtained blood sample. Such gas diffusion primarily occurs through the filter, although there is some diffusion past the wall of the syringe barrel. In achieving these important objectives, it is also important to provide an arterial blood gas syringe that can be made with few, and relatively inexpensive parts, while the assembly time associated therewith is minimized and the cost of assembly is also reduced. Although known prior art arterial blood gas syringes function satisfactorily for their intended purpose, it still remains desirable to provide an arterial blood gas syring that improves on the desired furnctions associated with such a syringe while keeping the cost of such a syringe to a minimum.
An arterial blood gas syring is disclosed in U.S. Pat. No. 4,424,817 to Williams, issued Jan. 10, 1984, entitled "Syringe With Means For Automatically Sealing A Blood Sample Within The Syringe" and assigned to same assignee as is the present invention. This syringe includes a sealing plug having a number of longitudinal channels formed about the circumference thereof. In communication with each of the longitudinal channels is a lateral channel that communicates with the interior of the sealing plug. Because of the higher pressure required to move blood along the relatively small area of the channels, as well as the fact that the surface of the blood is not easily broken because of the conical-shaped tip of the sealing plug, the blood will tend to fill the blood receiving space before it moves along the channels to any great extent. The plunger rod of this syringe has a cavity for receiving an elongated, cylindrical-shaped filter. The plunger rod is hollow for use in providing an air passageway to the outside environment from the filter. In cases in which it is desirable to aspirate blood into the syringe, the open end of the hollow plunger rod is closed off by the thumb or finger of the syringe user to prevent communication between the atmosphere and the inside of the hollow plunger rod. The plunger rod is then withdrawn creating a vacuum in the blooc receiving space so that the arterial blood is drawn therein.
U.S. Pat. No. 4,466,446 to Baidway, et al., issued Aug. 21, 1984, entitled "Plunger Assembly For Blood Gas Syringes" and assigned to the same assignee as is the present invention discloses an arterial blood gas syringe characterized by a particular construction for achieving aspiration. It is presently common practice to preset the sealing plug and plunger rod at a desired or predetermined position in the syringe barrel to define the blood receiving space. If, when taking a blood sample, the patient's arterial blood pressure is insufficient to cause a complete filling of the defined blood receiving space then aspiration can be achieved by retracting the plunger rod. By pulling back on the plunger rod the opposing surfaces of the sealing plug and plunger rod contact each other thereby forming a seal which terminates the air pathway between the outside atmosphere and the blood receiving space. Further retraction of the plunger rod produces lower pressure in the blood receiving space which causes the arterial blood to be drawn therein. This syringe also includes a filter for use in permitting the passage of air while stopping the flow of blood. This filter is located within the interior of the sealing plug and is measurably spaced from the upper surface of the sealing plug. The sealing plug of the syringe also has longitudinally-extending grooves formed about the circumferential periphery thereof. These grooves communicate with laterally-extending passageways, which communicate with the interior of the sealing plug.
In addition to the foregoing known blood gas syringes, representative of commercially available syringes, are the Bard-Parker ABG Mini-Kit syringe package and the PREZA-PAK II sampler syringe of Terumo Corporation. The Bard-Parker syring is characterized by a filter that is joined to an outer surface of a sealing plug and extends outwardly into the blood receiving space from the sealing plug. The filter is disc-shaped and has a diameter substantially corresponding to the inside diameter of the syringe barrel. The filter also has a stem section, which is integral with the disc-shaped section. The stem is received in a hole formed in the sealing plug to connect the filter to the sealing plug. The Terumo arterial blood gas syringe includes a sealing plug having a recessed cavity communicating with the blood receiving space and defined by a circumferential wall of the sealing plug. The circumferential wall fans outwardly in a direction towards the blood receiving space whereby the thickness of the wall decreases in a direction towards the blood receiving space. A filter is located within the recessed cavity, with the upper surface thereof completely exposed to the blood receiving space and spaced from the upper edge of the sealing plug. Like the syringe disclosed in U.S. Pat. No. 4,424,817, this syringe includes a hollow plunger rod in which aspiration can be achieved by preventing communication between the outside environment and the filter by closing off the plunger rod passageway.